Do sexual ornaments demonstrate heightened condition-dependent expression as predicted by the handicap hypothesis?

Abstract

The handicap hypothesis of sexual selection predicts that sexual ornaments have evolved heightened condition–dependent expression. The prediction has only recently been subject to experimental investigation. Many of the experiments are of limited value as they: (i) fail to compare condition dependence in sexual ornaments with suitable non–sexual trait controls; (ii) do not adequately account for body size variation; and (iii) typically consider no stress and extreme stress manipulations rather than a range of stresses similar to those experienced in nature. There is also a dearth of experimental studies investigating the genetic basis of condition dependence. Despite the common claim that sexual ornaments are condition–dependent, the unexpected conclusion from our literature review is that there is little support from well–designed experiments.